Steaming is an ancient form of cooking. The basic principle of steaming is to place the food above boiling water so that the rising steam provides heat to the food. Generally, a lid is placed over the water reservoir in which the food is supported so that the steam does not escape from the system.
For a variety of reasons, steam cooking is very popular today. For example, a heat source may be conserved because only enough heat to boil a small amount of water is required. Also, more food vitamins and minerals are retained by steam cooking than by placing the food in boiling water. In steam cooking, the steam surrounds and gently cooks the food in moist intense heat. Steaming avoids the harsh treatment that occurs when food is placed directly in boiling water and important food content is thrown away with the cooking water. Furthermore, many people prefer the fresh color and crisp texture of food prepared by steaming.
The steamers is use today are not ideally configured for use in a microwave oven. For example, the reservoir holding the water should be transparent to microwave energy but capable of withstanding high temperatures. Also, the food should be substantially shielded from the microwave energy so that substantially all of the microwave energy is used to heat the water.